This invention relates in general to mechanisms for raising and lowering a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle. In particular, this invention relates to a double cylinder assembly for raising and lowering such a tailgate that is pivotably supported on the dump box.
A typical dump truck includes a dump box that is movable (usually by pivoting) between a lowered position (for storing and transporting items) and a raised position (for dumping the items out of the dump box). A typical dump box includes a floor, a pair of side walls, a front wall, and an open rear end for accomplishing this function. Frequently, the open rear end of the dump box includes a pair of upstanding corner posts that are each formed from a hollow rectangular member. A tailgate is supported on the side walls of the dump box adjacent to the open rear end for pivoting movement between a closed position (wherein the tailgate closes the open rear end of the dump box for facilitating the storing and transporting of the items therein) and an opened position (wherein the tailgate is pivoted away from the open rear end of the dump box for facilitating the dumping of the items out of the dump box).
In many instances, the tailgate is affirmatively moved between the opened and closed positions by means of a cylinder (typically a pneumatic cylinder) that extends between the dump box and the tailgate. When the cylinder is extended, the tailgate is pivoted away from the open rear end of the dump box to the opened position. When the cylinder is retracted, the tailgate is pivoted toward the open rear end of the dump box to the closed position. In this manner, the operation of the cylinder controls the movement of the tailgate between the opened and closed positions.
In the past, the cylinder has typically been provided on the dump truck in one of two locations. In a first generally vertical orientation, a cylinder has been located within either or both of the hollow upstanding corner posts provided on the open rear end of the dump box. This generally vertical orientation is desirable because it does not expand the overall width of the vehicle, which can be limited by practical considerations or by regulation. However, the internal space that is available within each of these corner posts is limited, thus limiting the size of the cylinder that can be provided within each of the corner posts (and, as a result, the amount of force that is available to move the tailgate between the opened and closed positions) is relatively limited. In a second generally horizontal orientation, a cylinder has been located on the outside of either or both of the side walls of the dump box. This generally horizontal orientation is desirable because it is simple and inexpensive to install. However, as mentioned above, it does undesirably expand the overall width of the vehicle. Thus, it would be desirable to provide an improved mechanism for raising and lowering a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle that avoids these problems.